This invention relates to collision avoidance systems for vehicles such as aircraft, and more particularly to improvements on the invention described and claimed, in U.S. Pat. No. 4,768,036 issued in the names of George B. Litchford and Burton L. Hulland, entitled Collision Avoidance System.
The earlier invention provides methods of and means for repeatedly determining the positions of Own and Other transponder-equipped craft within the common service areas of two or more identified SSRs at known locations utilizing standard ATCRBS interrogations and replies thereto received at Own station. To initiate operation, Own's current position must be known or determined. This may be done by use of a trial and error method such as a Simplex algorithm, as described in U.S. Pat. No. 4,768,036. Such method enables completely passive operation, with no radio transmissions other than those already present in the normal operation of ATCRBS.